1. Field of the Invention
This disclosure relates to a vacuum circuit breaker, and particularly, to a flexible shunt for providing a conductive path between a movable electrode side and a main circuit terminal in a vacuum circuit breaker.
2. Background of the Invention
A vacuum circuit breaker is a kind of electric power equipment for opening or closing a conductive path of an ultrahigh voltage to high voltage of a power station or an electric power substation and protecting a circuit and an electric load side devices connected to the circuit by breaking the circuit upon occurrence of a fault current on the circuit.
In general, a vacuum circuit breaker is embedded in a distributing board, which includes an instrument and monitoring device such as a digital relay, and a plurality of circuit breakers, for monitoring states of the electric power and lines.
Since the vacuum circuit breaker is typically used by being embedded in the distributing board, a pull-out type vacuum circuit breaker having a carriage, which is movable for facilitation of installation and maintenance thereof.
The pull-out type vacuum circuit breaker roughly includes, for each of three phases (poles), a circuit breaker main body (abbreviated as main body hereinafter) provided with a contact part called as a vacuum interrupter, a switching mechanism for opening or closing the contact part, and a terminal part electrically connected to the contact part, the main body movable by the carriage having wheels, and a cradle for supporting the main body, the cradle having a first terminal part connected to the terminal part of the main body, and a second terminal part electrically connected to an external electric power circuit, the cradle fixed into a power distributing board.
Hereinafter, description will be given of an outer appearance of the main body of the pull-out type vacuum circuit breaker according to one exemplary embodiment with reference to FIG. 1. The cradle is a housing having the first terminal part and the second terminal part, and less relevant to the present disclosure. So, the cradle will not be illustrated and described in detail.
As shown in FIG. 1, a main body 100 may be installed on a carriage having wheels (no reference number given) to be movable back and forth. The main body 100 may include a front cover 10, a main body housing 20, a main circuit part 30 and terminal parts 32a and 40a. The terminal parts 32a and 40a may include an upper terminal 32 and a lower terminal 40 to be explained with reference to FIG. 2, and finger contactors of terminal end portions (no reference numeral given) of the upper terminal 32 and the lower terminal 40.
The main body 100 may be movable to a connected position at which the terminal parts 32a and 40a are connected to the first terminal part of the cradle, a test position at which the terminal parts 32a and 40a are separated from the first terminal part of the cradle due to the main body 100 being drawn out by the carriage but a electric power supply and signal line connection are maintained with respect to a controller (i.e., a controller (no reference numeral given) located at the rear of the front cover 10 of FIG. 1, and called as Over Current Relay (OCR) in the related field), and a disconnected position at which the main body 100 is further drawn out by the carriage such that the terminal parts 32a and 40a are separated from the first terminal part of the cradle and the electric power supply and signal line connection with respect to the controller are disconnected.
The present disclosure relates to a flexible conductor, so-called a flexible shunt, which provides a flexible electric connection unit for electrically connecting a movable shaft, which is connected to a movable contact, and a terminal and simultaneously allows for movement of the movable shaft. Hereinafter, description will be given of the corresponding flexible shunt according to the related art with reference to FIG. 2.
A main circuit part 30 having the related art flexible shunt includes a vacuum interrupter 33 as a contact part, an upper terminal 32 and a lower terminal 40 electrically connected to a stationary contact 34 and a movable contact 35 of the vacuum interrupter 33, respectively, a movable shaft 35a (so-called movable electrode) 35a, a connection rod 41 and a push rod 42 acting together as a vertical driving unit to vertically drive the movable contact 35 to a connected position where the movable contact 35 contacts the stationary contact 34 or a connected position where the movable contact 35 is separated from the stationary contact 35, a link 44 acting as a driving unit disposed at the main body side of FIG. 1 to transfer a switching driving force from a switching mechanism (not shown) to the vertical driving unit, a contact spring to apply contact pressure to the push rod 42 upwardly in the drawing such that the movable contact 35 maintains the contact state at the connected position, a clamp 36 having the movable shaft 35a inserted therein for heat emission to prevent overheat of the movable shaft 35a, a heat sink 37 integrally installed on the clamp 36, and a flexible shunt 38′ having one end connected to the clamp 36 and the other end connected to the lower terminal 40 so as to electrically connect the lower end 40 and the movable contact 35 to each other. A reference number 31 designates a main circuit part housing as a housing for accommodating those components of the main circuit part 30.
In the vacuum circuit breaker according to the related art, the flexible shunt 38′, which electrically connects the movable shaft 35a connected to the movable contact 35 to the lower terminal 40, is configured by twisting several strands of copper wires or stacking and pressing several sheets of copper thin plates.
As the vacuum circuit breaker became larger, an amount of current increased, which resulted in an increase in a thickness of the flexible shunt 38′. However, since the flexible shunt 38′ should be moved with the one end being connected to the clamp 36, which moved together with the movable shaft 35a, flexibility was required. Hence, a length of the flexible shunt 38′ increased for ensuring the flexibility.
However, the related art flexible shunt 38′ caused an increase in the size of the vacuum circuit breaker due to the increase in its length, which resulted in an increase in a fabricating cost of the vacuum circuit breaker.